Die devices having rotatable die bars are well known. These devices are comprised of a body member having a flat and horizontally oriented upper surface. A pair of elongated die bars typically are mounted in or on the body in a contiguous side-by-side manner engaging each other at a position which is aligned with the direction of the bending punch. The die bars have flat upper surfaces which lie in a common plane and in alignment with the flat upper surface of the body member.
This flat upper surface of the body member and the die bars provide a flat contact surface for the metal stock which is to be bent. When the bending stamp or punch is moved or driven against the metal stock in the area along the contiguous edges of the die bars, the die bars rotate to form a V-shaped groove and cause the metal stock to be bent to the desired angle.
One of the advantages of a die device with rotatable die bars is that it bends the metal stock without damaging or marking it. In contrast, die devices which utilize fixed V-shaped female dies have the disadvantage of producing distinctively perceptable and objectionable marks on the metal stock along the bend in the area at which the metal stock engages the die when the bending punch is driven into the die to produce the bend.
Die devices having rotatable die bars, rather than V-shaped dies are not, however, without limitations. For example, in the known die devices which have rotatable die bars, the edge of the metal stock to be bent must reach beyond the line along the center of the flat upper surface of each die bar (i.e., beyond the line parallel to the axis of rotation of each die bar). In the known die devices, each die bar rotates freely and independently of the other. Where a punch is moved or driven against a piece of metal stock, one end of which does not reach beyond the center of the flat upper surface of one of the die bars, that die bar will be permitted to turn away freely. As a result, the metal stock is either not bent at all, or not bent to the desired angle.
This requirement has proven to be a considerable limitation in the use of these types of die devices because it is often necessary (especially to attain greater rigidity) to produce bent metal stock in which the leg lengths are shorter than the radius of the die bars.